STROBE Statement—checklist of items that should be included in reports of observational studies

Title and abstract

ItemNo.
1

Recommendation(a) Indicate the study’s design with a commonly used term in the title or the abstract(b) Provide in the abstract an informative and balanced summary of what was done and what was
found

Introduction
Background/rationale

2

Explain the scientific background and rationale for the investigation being reported

Objectives

3

State specific objectives, including any prespecified hypotheses

Methods
Study design

4

Present key elements of study design early in the paper

Setting5

Describe the setting, locations, and relevant dates, including periods of recruitment, exposure,Participants

6(a) Cohort study—Give the eligibility criteria, and the sources and methods of selection offollow-up, and data collection
participants. Describe methods of follow-up
Case-control study—Give the eligibility criteria, and the sources and methods of caseascertainment and control selection. Give the rationale for the choice of cases and controls
Cross-sectional study—Give the eligibility criteria, and the sources and methods of selection ofparticipants(b) Cohort study—For matched studies, give matching criteria and number of exposed andunexposed
Case-control study—For matched studies, give matching criteria and the number of controls percase
Variables

7

Clearly define all outcomes, exposures, predictors, potential confounders, and effect modifiers.
Give diagnostic criteria, if applicable

Data sources/8*

measurement

For each variable of interest, give sources of data and details of methods of assessment(measurement). Describe comparability of assessment methods if there is more than one group

Bias

9

Describe any efforts to address potential sources of bias

Study size

10Explain how the study size was arrived atContinued on next page

1PageNo.

Relevant text frommanuscriptQuantitative

11variables
StatisticalExplain how quantitative variables were handled in the analyses. If applicable, describe whichgroupings were chosen and why

12methods(a) Describe all statistical methods, including those used to control for confounding(b) Describe any methods used to examine subgroups and interactions(c) Explain how missing data were addressed(d) Cohort study—If applicable, explain how loss to follow-up was addressed
Case-control study—If applicable, explain how matching of cases and controls was addressed
Cross-sectional study—If applicable, describe analytical methods taking account of samplingstrategy(e) Describe any sensitivity analyses

Results
Participants

13*(a) Report numbers of individuals at each stage of study—eg numbers potentially eligible, examinedfor eligibility, confirmed eligible, included in the study, completing follow-up, and analysed(b) Give reasons for non-participation at each stage(c) Consider use of a flow diagram

Descriptive data

14*(a) Give characteristics of study participants (eg demographic, clinical, social) and information on
exposures and potential confounders(b) Indicate number of participants with missing data for each variable of interest(c) Cohort study—Summarise follow-up time (eg, average and total amount)

Outcome data

15*

Cohort study—Report numbers of outcome events or summary measures over timeCase-control study—Report numbers in each exposure category, or summary measures of exposure
Cross-sectional study—Report numbers of outcome events or summary measuresMain results

16(a) Give unadjusted estimates and, if applicable, confounder-adjusted estimates and their precision(eg, 95% confidence interval). Make clear which confounders were adjusted for and why they wereincluded(b) Report category boundaries when continuous variables were categorized(c) If relevant, consider translating estimates of relative risk into absolute risk for a meaningful time
periodContinued on next page2

Other analyses

17

Report other analyses done—eg analyses of subgroups and interactions, and sensitivity analyses

Discussion
Key results

18Summarise key results with reference to study objectives

Limitations

19

Discuss limitations of the study, taking into account sources of potential bias or imprecision. Discussboth direction and magnitude of any potential bias

Interpretation

20

Give a cautious overall interpretation of results considering objectives, limitations, multiplicity ofanalyses, results from similar studies, and other relevant evidence

Generalisability

21

Other information
Funding
22

Discuss the generalisability (external validity) of the study results
Give the source of funding and the role of the funders for the present study and, if applicable, for theoriginal study on which the present article is based*Give information separately for cases and controls in case-control studies and, if applicable, for exposed and unexposed groups in cohort and cross-sectional studies.
Note: An Explanation and Elaboration article discusses each checklist item and gives methodological background and published examples of transparent reporting. The STROBE
checklist is best used in conjunction with this article (freely available on the Web sites of PLoS Medicine at http://www.plosmedicine.org/, Annals of Internal Medicine at
http://www.annals.org/, and Epidemiology at http://www.epidem.com/). Information on the STROBE Initiative is available at www.strobe-statement.org.

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